Apparatus for making plywood tubing



Nov. 13, 1951 T. E. ILCH APPARATUS FOR MAKING PLYWOOD TUBING 3 Sheets-Sheet 1 Original FiledSept. 10, 1942 INVENTOR. THEODORE f. lLCf/ Nov. 13, 1951 T. E. lLCH 2,574,920

APPARATUS FOR MAKING PLYWOOD TUBING Original Filed Sept. 10, 1942 5 Sheets-Sheet 2 Fig. 4

INVEN TOR. THEODORE E. ILCH NOV. 13, I ILCH APPARATUS FOR MAKING PLYWOOD TUBING 3 Sheets-Sheet 3 Original Filed Sept. 10, 1942 I I I I I I INVENTOR. THEODORE E. lLCH BY j Patented Nov. 13, 1951 APPARATUS FOR MAKING PLYWOOD TUBING Theodore Edward Ilch, Hempstead, N. Y., assignor to United States Plywood Corporation, New York, N. Y., a corporation of New York Original application September 10, 1942, Serial No. 457,894. Divided and this application December 29, '1945, Serial No. 638,337

8 Claims. (Cl. 144-281) 1 The invention relates to plywood fabricated into the form of a pipe or tubing and more particularly to seamless plywood tubing and pertinent apparatus. Seamless, as hereinafter used throughout this specification, is intended to indicate the absence of any'deflnite line of juncture extending from the interior to the exterior surface of the pipe or tubing. This application is a divisional application of Ilch application, S. N. 457,894, filed September 10, 1942, for Method and Apparatus for Making Plywood Tubing, which became Patent No. 2,411,542, dated November 26, 1946.

An object of the invention is to produce such plywood tubing having the inherent advantages of plywood, but which by reason of its tubular form has extremely valuable industrial applications, for instance, as a structural member constltuting a strong column or, by reason of its great strength in hoop tension as a pipe for conveying fluids under pressure. A further object of the invention is to provide a plywood tube whose length is considerably greater and in fact may be many times greater than the maximum transverse dimension of the tube, the tube being built up from individual veneer units. It is also an object of the invention to providean improved process and apparatus for the manufacture of such plywood tubing wherein the individual veneer units are not subjected to any peripheral compressive stresses during their assembly and particularly during the molding operation. Other objects will become evident from the further, more detailed description of the invention.

While attempts have been made by prior art workers to produce a more or less seamless plywood pipe or tubing, for instance by assembling such pipe or tubing from lumber or fiat or bent plywood, such attempts have not been productive of a commercially utilizable tubing because of the inherent stresses characterizing the material thus produced and because an inordinate amount of assembly work is involved in the production of such material. The primary cause of failure of such a product to take its place in industrial applications, however, has been its deiiciency in strength both in the longitudinal direction and the transverse direction of the pipe. Furthermore, besides the unsatisfactory nature of the product heretofore produced, the fabrication involved extremely high costs and com-paratively small production yield.

In accordance with my invention, I can produce economically and with excellent results so are concerned, a variety of sizes of plywood p p or tubing in lengths up to as much as 11 feet, so that these comparatively long structures can be used as a strong column, for instance, in the production of radio antenna masts. The tubing is characterized by great strength in a transverse direction and therefore considerable strength in hoop tension, thus being ideally suited for conveying fluids under considerable pressure. The strength of the tubing is controlled by the manner in which the grain is made to run.in the layers of veneer. If the preponderance of grain of the wood is laid up to run longitudinally, the finished tubing will be preferably of value for use as a column, whereas if the preponderance of the veneer grain is made to run around the pipe, it will be more useful for carrying fluids under pressure. Obviously, for particular commercial applioations, intermediate efiects of strength can be secured, for instance by altering the thickness of the tubing or the number of veneers of which the tubing is constituted.

In its broadest aspects, my invention consists in the building up, and molding in its final and ultimate shape, a pipe or tubing, that is, hollow structures whose length is considerably greater than their diameters, by rolling up cylindrically into loose tubes, separately and in succession, a plurality of layers of veneers of plywood which have been suitably provided with layers of adhesive, sliding the thus rolled layers of veneers individually and successively inside a longitudinally split steel mandrel of suitable length through one of its two open ends, contracting the split mandrel to enable the finished article to be withdrawn more readily after the molding and after release of the mandrel, inserting a flexible fluid-tight membrane in the shape of a cylindrical tube inside the assembled veneers within the steel mandrel, and after placing the aggregate of mandrel, veneers, and membrane into a fluid pressure chamber, sealing the aggregate therein, applying heat and pressure by means of the membrane to the built-up veneers to cause the activation of the adhesive, with which it has been previously impregnated or coated, to thereby produce the plywood tubing.

A particular embodiment of my novel process of producing a plywood tubing and of an apparatus suitable for carrying out such process, are illustrated in the accompanying drawings, in which Fig. 1 is a perspective view of a steel mandrel or split tube into which the veneers in the carrying out of my process are adapted to be far as the necessary characteristics of strength placed.

Fig. 2 is a cut-away view, also in perspective. showing the steel mandrel. the tubing constituted of a plurality of veneers in position within the mandrel, and the fluid-tight membrane or rubber fabric sleeve within the tubing. 1

Fig. 3 is an end view or section showing in concentric arrangement an outside casing with the split steel mandrel and its contents positioned therein.

Fig. 4 is a cut-away view showing the mandrel, ready for molding of the tubing therein, in position in the outside or cooking casing.

Fig. 5 is a schematic showing of the outside casing and necessary plumbing for the heat and pressure treatment.

Fig. 6 is a. section through the outside casing or cooker with a modified sealing arrangement for the veneers in the split mandrel.

Referring more particularly to the drawings. in which similar reference characters identify similar parts in the several views, sheets of plywood veneer coated with a suitable adhesive, after drying, are curled or rolled up cylindrically and slid one after the other into the split steel mandrel II! which is provided throughout its length with a slot ll of suitable width. The sheets of veneers are accurately templated to the proper width so that when they are slipped into the steel mandrel, through one of its open ends, they will expand against and completely overlie the interior surface thereof, having neither an overlapping nor an appreciable gap between their adjacent free edges after they are forced into place. Each layer of veneers is accordingly a little narrower than the preceding layer slid into the mandrel.

The butt Joints in the several layers of veneers are very carefully arranged so that they do not occur at exactly the same point in the periphery of the tubing to be formed, but are distributed at various points throughout the periphery of the tubing. As a plurality of layers of veneers are used for the tubing, the completed molded tube will be. to all intents and purposes. seamless.

After successive sheets of veneers have been slid into the steel mandrel l0 and all of the plies are in place, clamps l2, distributed appropriately throughout the length of the steel mandrel, are tightened by the bolts I3, giving the mandrel the exact inside diameter desired, and which will be the outside diameter of the plywood tubing to be produced. The layers of veneers'within the steel mandrel constitute the pipe M and will, after the heat and pressure treatment hereinafter described, form the molded.

plywood tubing. It will be understood that at the time that the mandrel is contracted, the

veneers lie loosely within the mandrel. with many and considerable spaces between the individual veneers and between the first veneer and the mandrel. The degree of contraction of the mandrel is very small and is insumcient to create any peripheral compressive forces in any of the veneers. As already indicated, the purpose of the contraction of the mandrel is to provide a slight clearance between the same and the finished tube upon release of the mandrel at the end of the process.

A flexible, rubberized fabric or similar fluidtight membrane in the shape of a cylindrical tube or sleeve I! and which has both of its ends open. and is longer than the split steel mandrel II, is then slipped or threaded into the steel mandrel within the assembled veneers, the ends of the sleeve being doubled back for a short distance over the outside of the mandrel, as shown at I! in Fig. 4, and an outer ring or sleeve ll is slipped on the folded back ends of the membrane to hold the fabric in place.

The mandrel assembly, now containing the plywood veneers and the sleeve, is then placed in position within an outer casing l8, being substantially centrally disposed therein by resting on a, cradle l9. The mandrel assembly is pushed into the outer casing it until the end of the mandrel iii abuts tightly against a gasket 20 positioned within and bearing against the head 2i of the casing i8. At the other end of the outer casing a companion plate 22, having a et 28 on its inner face is pressed against the end of the mandrel it, a plurality of bolts 25 being used to press the companion plate 22 toward the end plate 25 of the casing. The bolts 26 being drawn up on the end plate, a tightening and of both ends of the mandrel I0 is accomplished. In this manner, the whole of the sleeve it of the fluid-tight or rubberized fabric is sealed, except for an aperture 28 in the center of the gasket 23 and a like aperture 21 in the gasket 20 at the head end of the casing it. These apertures 26 and '21 are for the admission and egress of the heating and cooling fluids.

After the sealing, thus accomplished, if fluid under pressure is admitted at one end, and the other end is closed, the bag or sleeve It will be distended, forcing the veneers tightly against the interior surface of the mandrel It while the latter is in the transversely contracted condition. If these veneers have been previously coated with a heat-sensitive adhesive and if the fluid introduced is suflibiently hot to activate the adhesive. the veneers will be tightly bound together. Pressure resulting from heating of air or generation of vapor in the fibrous layers. is relieved through the narrowed slot H which still remains in the mandrel after contraction, as shown in Fig. 3.

After sufllcient exposure to heat has been obtained, the end plate 22 can be removed and the split tube or mandrel can be withdrawn from the outside steel casing. If the clamping device or clamps are then released, the mandrel will spring to its normal. larger diameter. the plywood tube which has been made can be withdrawn and is ready for treatment, assembly into useful articles or for sale without further treatment.

Describing the operations above outlined, and referring now particularly to Fig. 5. when the sealing, as above described. has been completed,

air-valve 28 and inlet valve 29 are opened, the exhaust valve 30 being closed. Exhaust valve ii is generally left open. Air pressure through t1 inlet valve 29 is permitted to enter the casin until the pressure, as indicated by air pressure gage I2, is sumcient to cause the veneers inside the mandrel ll to snap into place. An air pressure of approximately 50 pounds per square inch has been found in practice to be adequate for this purpose. The air valve 28 is then closed and the steam valve 33 is opened. Exhaust valve 30 is opened at the same time as the steam valve 33. The steam passing into the casing through the inlet valve 29 and inlet pipe 34 forces the air out, the temperature rising, as indicated by the thermometer 35. to approximately 300 F. The pressure is maintained purely by the pressure of the steam, or if it is desired to have the pressure higher without increasing the temperature. additional air may be admitted through the valve 28. A continual draining or bleeding of the system is permitted through the exhaust valve 30 to prevent stratification and to maintain the desired temperature.

The outside casing II is provided at a number of points throughout its length with vents 3!, which permit any pressure built up between the outer casing II and the steel mandrel II to be continuously relieved. I have found that a minimum of two of these vents or small holes in the outer casing i8 is desirable for the proper carrying out of my process.

After asufllcient amount of heat has been imparted to the assembly within the casing to activate the thermo-sensitive adhesive, cooling in any suitable manner is effected if the adhesive or glue is a thermo-plastic adhesive. If the adhesive or glue used is thermo-setting, it is only necessary to release the pressure. The mandrel II is then removed from the outer casing II, the clamps l2 loosened, the sleeve I! removed, and the finished plywood tubing withdrawn from the steel mandrel it.

The sizes of plywood tubing which may be fabricated in accordance with my process are limited only by the expediency and feasibility of handling and by the size of the apparatus. Plywood tublngs in sizes ranging from one-half inch to six inches outside diameter have been produced successfully by means of the apparatus and in accordance with the steps hereinabove described. Apparently, there is no limit to the diameter of the tubing except by convenience in handling and in the size of suitable apparatus. For instance, plywood tubing up to twenty-four inches outside diameter could be readily produced. So far as lengths are concerned, up to eleven feet have been in commercial production and in larger di ameters even greater lengths can be produced with facility, economy, and satisfactory results, from the point of view of strength in both 1ongltudinal and transverse directions.

While I have described hereinabove a specific embodiment of my invention, it is obvious that various changes in the specific arrangement of the several parts of the apparatus may be made without departing from my invention. For instance, in place of the flexible fluid-tight membrane or sleeve it open at both ends necessi tating the doubling back of the excess at each end, there may be used a cylindrical tube very much like an automobile inner tube with both ends sealed. With such alternative structure, a valve stem would be utilized at each end havin different sealing mechanism than that described.

In Fig. 6. I have shown in schematic cross-section, as the layers of veneers are omitted, such an alternative structure for attaining the sealing of the mandrel and veneers. In such alternative structure, a cylindrical pressure tube 40 of material, for instance rubber, such as is used in an automobile inner tube, is sealed at both ends, all

- seams of the tube being vulcanized, a valve stem Ii being provided at each end of the tube. The tube can then be inflated to distend the same against the layers of veneers by air/or steam pressure admitted and exhausted through valves 42 and subsequently deflated. The split mandrel it, into which the veneers and sleeve or tube 40 have been placed is supported within the outer cooking casing in substantially the same manner as heretofore described in connection with the preferred embodiment of the apparatus.

Aside from the specific variation just described, other alternative forms of structure and details will be apparent to those skilled in the art. For

instance, while I have described a specific at" 75 application of heat and pressure to the veneers to bring them to the final molded condition by the activation of the glue.

It will be seen from the foregoing that I have provided a process for manufacturing plywood tubing wherein the tube is built up from a plurality of pliable veneer units which are inserted one by one. and endwise, into a relatively long, longitudinally split mandrel, the mandrel having substantially the outer contours and dimensions of the finished plywood article; and that in the course of the telescoping assembly of the veneer units preparatory to the inflation of the flexible membrane and likewise during the course of the molding, the veneer units are not subjected to any peripheral compression, 1. e., no force is exerted on them from the outside to compel them to contract peripherally, the veneer units being at most subjected, aside from the radial pressure or the pressure normal .to their surfaces, to a slight peripheral tension. Thereby buckling 0f the veneers is avoided while at the same time overlapping at the joints of the individual veneers is insured against.

WhatIclaimis:

i. In an apparatus for forming an integral, molded, seamless plywood tube, the combination of an integral, resilient open-ended, tubular mandrel having a narrow slot therein extending from one end thereof to the other, said mandrel being completely open and unobstructed at least at one end so as to be capable of receiving endwise a plurality of tubularly coiled layers of wood veneers, means for contracting the mandrel peripherally whereby the width of the slot is reduced, and means for applying heat and pressure to said layers of wood veneers from the interior outwardly and while they are confined within said mandrel to mold them to the tubular shape of the contracted mandrel, said mandrel expanding resiliently to its original, unrestrained con dition on release of the contracting means when the molding operation is completed.

2. An apparatus for forming an integrai, molded, seamless tube of flbrous sheet material. comprising a. resilient tubular, metallic mandrel having a slot extending from one end thereof to the other, said mandrel being completely open and unobstructed at least at one end soas to be capable of receiving endwise a plurality of tubu larly coiled layers of wood veneers, means for contracting the mandrel peripherally whereby the width of the slot is reduced, a chamber, means for supporting said mandrel within the chamber, and means for applying heat and pressure to the interior of the mandrel, said mandrel springing resiliently to its original unrestrained condition on release of the contracting means when the molding operation is completed.

3. An apparatus for forming an integral, molded, seamless plywood tube, comprising a one-piece, resilient, tubular steel mandrel, having a slot running from one end thereof to the other, said mandrel being completely open and unobstructed at least at one end so as to be capable of receiving endwise a plurality of tubularly coiled layers of wood veneers, means for contracting the mandrel peripherally, an inflatable, tubular, open-ended membrane insertable within the mandrel. an outer casing for receiving the mandrel with the membrane therein, means for sealing the membrane against the space about the mandrel, and piping for introducing a heated fluid medium into the interior of the membrane, said mandrel springing resiliently to its original, unrestrained condition on release of the contracting means when the molding operation is completed.

4. An apparatus. for forming an integral, molded, seamless plywood tube, comprising a one-piece, resilient, tubular steel mandrel, having a narrow longitudinal slot running from one end thereof to the other, said mandrelbeing open at both ends and unobstructed so as to be capable of receiving endwise a plurality of tubularly coiled layers of wood veneers having adhesive applied thereto, means for contracting the mandrel peripherally, comprising a flat metal band and a take-up bolt and nut, an inflatable, tubular, open-ended membrane. insertable within the mandrel, an outer casing, a cradle type support secured to the inside of the casing at the bottom thereof for receiving the mandrel with the membrane therein, means for sealing the membrane against the space about the mandrel, said sealing means comprising a companion plate, secured to said outer casing, and a gasket cooperating to close the end of said membrane, and piping for introducing a heated fluid medium into the interior of the membrane, said mandrel being adapted to spring resiliently to its original, unrestrained condition on release of the contracting means when the molding operation is completed.

5. An apparatus for forming an integral, molded, seamless plywood tube, comprising a one-piece, resilient, tubular steel mandrel, having a slot running from one end thereof to the other, said mandrel being completely open and unobstructed at least at one end so as to be capable of receiving endwise a plurality of tubularly coiled layers of wood veneers, means for contracting the mandrel peripherally, an inflatable, tubular, closed membrane insertable within the mandrel, an outer casing for receiving the mandrel with the membrane therein, and piping for introducing a heated fluid medium into the interior of the membrane, said mandrel springing resiliently to its original, unrestrained condition on release of the contracting means when the molding operation is completed.

6. An apparatus as set-forth in claim 4 further characterized by the sealing means and gasket having an opening therein whereby the heated fluid medium passes through the mandrel and at the same time exerts a certainpredetermined pressure on the veneers.

7. An apparatus for forming anintegral, molded, seamless plywood tube. comprising a one-piece, resilient, tubular steel mandrel, having a narrow longitudinal slot running from one end thereof to the other, said mandrelgbeing open at both ends and unobstructed so as-m be mandrel peripherally,

capable of receiving endwise a plurality of tubularly coiled layers of wood veneers having adhesive applied thereto, means for contracting the mandrel peripherally, comprising a flat metal band and a take-up bolt and nut, an inflatable, tubular, open-ended membrane insertable within the mandrel, an outer casing, means for sealing the membrane against the space about the mandrel, said sealing means comprising a companion plate, secured to said outer casing, and a gasket cooperating to close the end of said membrane. and piping for introducing a heated fluid medium into the interior of the membrane, said mandrel being adapted to spring resiliently to its original. unrestrained condition on release of the contracting means when the molding operation is completed.

8. An apparatus for forming an integral. molded, seamless plywood tube, comprising a one-piece, resilient, tubular steel mandrel, having a narrow longitudinal slot running from one end thereof to the other, said mandrel being open at both ends and unobstructed so as to be capable of receiving endwise a plurality of tubularly coiled layers of wood veneers having adhesive applied thereto, means for contracting the an inflatable. tubular, open-ended membrane insertable within the mandrel, an outer casing, a cradle type support secured to the inside of the casing at the bottom thereof for receiving the mandrel with the mempleted.

THEODORE EDWARD mm.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,428,469 Bolger Sept. 5, 1922 1,667,434 Norton Apr. 24, 1928 2,276,004 Vidal Mar. 10, 1942 2,296,781 Farny Sept. 22, 1942 2,312,382 Gramelspacher Mar. 2, 1943 2,343,225 Pray Feb. 29, 1944 2,372,738 Powell Apr. 3, 1945 BORMGN PATENTS Number Country Date 637,029 Germany Sept. 15, 1933 444,462 Great Britain Mar. 20, 1936 I 479.065 Great Britain Jan. 31, 1938 

